Cleaned up in preparation for next test

- Removed everything related to Top-Down or Third Person perspective (in
PlayerController & BuildingObject mainly)
- Rewrote ScenarioHandler to prepare for next Interface test
- Added a GameStateHandler to remove some code from PlayerController
- Simplified a bit of code which no longer needs to check for a player
on update
- Simplified the scene a bit by grouping "static objects" (ones that we
don't modify often)
- Removed old commented code from certain places
- Fixed a few typos